The Extraordinary Disorder of Obsidian

RUNNING SOUTH of the turquoise eye of Mono Lake just east of the Sierra’s steep escarpment are hills that once hissed and  groaned, gushed fountains of pumice and ash and sticky masses of incandescent lava. Today, wandering among the range of stubby volcanic hills leads you across piles of pumice that grind and crunch underfoot. Daliesque spires of black, lichen-spotted obsidian tilt like disfigured statues at strange angles into the sky. 

This land is a land of glass, fashioned during recent millennia from obsidian and pumice with the same chemical composition as granite. But there the similarities with granite end. The granitic rocks of the Sierra Nevada formed on the order of a hundred million years ago, whereas the obsidian craters just east of the mountain range erupted in the last few millennia, some in recent centuries. Making granite requires time enough for melt to cool slowly in the insulating warmth of Earth’s crust, enough time to allow for myriad  atoms vibrating within it to arrange them selves into proper crystals. No such leisure exists for melt that erupts at the surface. It is granite flash-frozen. It is a chaos, a pandemonium contained in stone. 

Obsidian, because it lacks the constraints imposed by an internal molecular order, can in fact be flaked into tools with edges many times sharper than a razor blade.

Imagine you are so small that you could enter the strange world within a shard of obsidian—a world of buzzing atoms: iron, magnesium, aluminum, calcium, sodium, and potassium spun out among tumultuous arrangements of silicon and oxygen. If only given more time, these atoms would have ordered themselves into the neat, patterned, geometric symmetry of crystals. Yet it is the pure, unbridled disorder of obsidian that makes it so extraordinary. When granite breaks, it cleaves along rough, ragged surfaces defined by boundaries between crystals and planes of molecular weakness within its constituent minerals. This interior order guides fractures and limits the acuteness of edges made by their intersections. It is different with obsidian. 

Consider by way of analogy two chocolate bars: one with a pattern of small squares impressed upon it, the other just a simple, unscored, uniform bar. When pressure is applied to each, the first will tend to break into little squares, but the second will break haphazardly into sharp edged fragments. Obsidian, because it lacks the constraints imposed by an internal molecular order, can in fact be flaked into tools with edges many times sharper than a razor blade. For this reason, volcanic glass, rather than surgical steel, is the material of choice for scalpels some plastic surgeons use. 

In the Sierra Nevada, we find flakes of obsidian, shards left by Indigenous hunters who worked the black volcanic glass into arrow points, their edges sharpened to translucence, to hunt animals that would sustain their loved ones. Throughout their  millennia of continuous presence in the Mono Basin, they would have witnessed volcanic eruptions birth the region’s pale hills. What stories did they tell, these hunters and their kin, on dark summer nights as they gazed upon the cradling arms of the Milky Way, of how the stone that took life and gave life came itself into life? What stories have we remembered? 

This essay is excerpted from The Paradise Notebooks: 90 Miles across the Sierra Nevada, by Richard J. Nevle and Steven Nightingale, published in spring 2022 by Cornell University Press and used here by permission. 

Richard J. Nevle is the deputy director of  the Earth Systems Program at Stanford University and recipient of the university’s highest teaching honor. He lives in San José, California.


  1. Most beautiful poetic language. Is it possible to get a copy?

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